In general, when a power supply circuit element such as a power module (a power module will be described below as a representative example of power supply circuit elements) is mounted on a printed circuit board in the circuit board unit, terminal pins of the power module are bonded to a printed wire (copper foil) of a main circuit on the printed circuit board. For example, an inverter module is used as the power module in a refrigerating apparatus (the refrigerating apparatus described herein includes an air conditioning apparatus). Such a power module is connected between an external power supply and an inverter compressor (target to be driven). Current supplied through terminal pins of the power module flows through copper foil of a main circuit of a printed circuit board and then is supplied to the compressor.
Recently, even high power modules have been reduced in size with improvement in performance of semiconductor devices. Thus, an interval between terminal pins provided on the power module tends to be narrowed. There is a power module directly soldered to a printed circuit board and rated at high current of 50-100 A. A small-size power module has a small cross-sectional area of a terminal pin, resulting in an increase in temperature of the terminal pin due to heat from a chip of the power module. In addition, the temperature in a connection part between a printed circuit board and the terminal pin increases and, as a result, exceeds the heat resistant temperature of the printed circuit board. Thus, there is a possibility that the printed circuit board cannot be used up to the rated current.
If, e.g., a circuit board unit used for an inverter control of the foregoing air conditioner is rated at the high current level described above, it is necessary to expand a cross-sectional area of a printed wire (copper foil) including the connection part to lower a resistance value. However, in order to lower the resistance value, it is necessary to expand the width of the copper foil because the thickness of the copper foil cannot be extremely increased.
The expansion of the copper foil width is contradictory to the narrowing of the interval between the terminal pins of the power module. Thus, it is not practical that, in the printed circuit board unit using the high power module having the narrow interval between the terminal pins, the width of the copper foil is expanded so that high current can flow through the printed circuit board unit.
Patent Document 1 discloses the configuration in which a terminal base to be bonded onto a printed circuit board is used as a connection member (10) of an electrical circuit and a terminal pin of a power module is screwed to the terminal base.